CSI-Dairy: Milk fat depression

Numerous ‘culprits’ exist on dairy farms, robbing herd performance and injuring the dairy’s bottom line. Identifying and arresting the offender isn’t always easy, and often requires a full investigation, gathering and analyzing evidence on the farm and in the lab. This month’s investigators uncover issues that might impact milk fat depression.

By Kevin Leahy

One of the herds we work with experienced a significant drop in butterfat and protein level. Butterfat levels on this 2,400-cow herd had dropped from 3.70% to 3.25%. Protein levels, while less significant of a drop, were down from 3.04% to 2.91%.

Historically the herd had been using crude starch as the only measurement of starch in the ingredients. The herd decided to conduct a rumen starch degradability test on the ingredients in the ration containing starch to see if they could find some answers as to why butterfat and protein levels were suppressed.

A near infrared (NIR) rumen degradable starch test is a quick and relatively simple test that, in this case, could either verify or eliminate rumen degradable starch as a cause of the milk fat depression. These analyses along with the dry matter contributed by each of the starch-containing ingredients allowed us to calculate exactly how much starch was being degraded in the rumen.

Starch affects rumen pH, microbial growth and can affect the overall health of the animal. Too much starch digested in the rumen can cause milk fat depression, reduced intakes and lower milk production.

A closer look at starch

Results from the test showed that the herd was feeding more rumen degradable starch than our proprietary calculator would consider optimal. As a result, rumen degradable starch was verified as a likely cause of the fat depression the herd was experiencing.

A look back at the herd’s feed purchases showed a recent change in feed ingredients to be the culprit. The herd had been presented with the opportunity to purchase lower-cost feed ingredients. On paper the ingredients had appeared to provide similar nutrients. The herd decided to purchase the ingredients, and unfortunately what looked to be a good move on paper resulted in depressed milk fat and protein levels.

Readjusting starch

After the herd knew the starch level of the ration ingredients from the insights the rapid starch test and calculator delivered, we were able to readjust the formulation. The herd backed off of the new ingredients and was able to feed the optimal starch level.

After the herd adjusted the ration to the new optimal starch level, butterfat levels returned to normal in just a couple of weeks. (See Figure 1.)

This herd continues to test starch levels on a regular basis. Rations are re-adjusted accordingly based on starch results, and the herd knows that it is not overfeeding or underfeeding in a particular area. It also gives the herd a better idea how the ration is going to react within the cow before it’s even fed.

Rumen degradable starch tests can help dairy producers find the right balance between milk production, milk components and economical feedstuffs. The insights garnered from rumen degradable starch testing could also potentially save money when it comes to purchasing feed, as producers can make a more informed purchase.

Every producer has different goals. It might be to have more consistent milk components, take advantage of less expensive input and feed sources or improve overall herd health. But when balancing rations to meet those goals, nothing is more important than an informed decision.